This invention relates to a discharge lamp lighting system which keeps the lamp lit by means of an intermittent booster which supplies reignition energy to the discharge lamp in each half cycle of an a.c. power source. The system combines a discharge lamp or lamps and a backswing booster generating an intermittent oscillation output at a given point of the lamp current and continuing for a portion of every half cycle of the power source, whereby a more economical and compact lighting device for any kind of discharge lamp is obtained.
Prior art discharge lamp lighting devices with a booster for applying a backswing voltage to start a discharge lamp are disclosed in U.S. Pat. Nos. 3,665,243; 3,753,037 and 3,866,088. Such known starter comprises mainly three oscillating circuits. A first oscillation circuit includes a power source, a linear inductor and a capacitor connected in series. A second oscillation circuit connected across the capacitor includes a saturable nonlinear inductor connected in series with a thyristor type voltage-responsive switching element. A third oscillation circuit comprises the nonlinear inductor and its distributed capacity. The discharge lamp is connected across the capacitor. The oscillation voltage generated across the capacitor for starting the discharge lamp is so high that a conventional glow starter may be substituted. The power source may be a d.c. or an a.c. source. Where the discharge lamp is of the hot cathode type which has a pair of filaments serving as discharge electrodes, the filaments are generally connected in series with the first oscillation circuit and/or with the second oscillation circuit for quickly heating the filaments. The foregoing references and remarks relate to a starter with a semiconductor.
The above references do not provide any teaching regarding a solid state lighting device. The economical aspects of compactness in structure and reliability of operation of a solid state discharge lamp lighting device are also not shown. In other words, the size of the current limiting means is essentially determined by the product VA (voltampere) of the terminal voltage (V) and the flowing current (A). Since the lamp current (A) is generally determined by the lamp type, a small size current limiting means may be used by reducing the terminal voltage (V). In conventional lighting systems, such as of the glow starter type or the previously proposed electronic starter type, the difference voltage between lamp voltage and starting voltage is indispensable for the current limiting means. Therefore, in the prior art the current limiting means cannot be reduced in size below a fixed minimum size. Adding the lead capacitor to the current limiting means does not provide a lighting device of enough compactness. Thus, the need for providing a miniaturized discharge lamp lighting device has not yet been satisfied. Though it is known to use the power factor improving impedance of a capacitor of 3.5 .mu.F connected in parallel to the power source in a lag lighting operation of a single 40-watt discharge lamp, whereby a source voltage of 200 volts and 60 Hz is employed, the miniaturization of the device is restricted to conventional means.